In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged, and exposed to a light pattern of an original image to be reproduced, to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "tones". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. The process is well known, and is useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum imaging that the toner and debris remaining on the surface be cleaned thoroughly therefrom.
Blade cleaning is highly desirable method for removal of residual toner and debris (hereinafter, collectively referred to as "toner") from a charge retentive surface. In a typical application, a relatively thin elastomeric blade member is provided and supported adjacent and transversely across the charge retentive surface with a blade edge chiseling or wiping toner from the surface. Subsequent to release of toner from the surface, the released toner accumulating adjacent the blade is transported away from the blade area by a toner transport arrangement or gravity. Unfortunately, blade cleaning suffers from certain deficiencies, primarily resulting from the frictional sealing contact which must be maintained between the blade and the charge retentive surface. Friction between the surfaces causes wearing away of the blade edge, and damaging wearing contact with the charge retentive surface. In addition to the problem of wear, which is more or less predictable over time, blades are also subject to unpredictable failures. The blade may flatten toner and cause impaction of toner on the surface. The impact from carrier beads remaining on the charge retentive surface subsequent to development may damage the blade, and sudden localized increases in friction between the blade and surface may cause the phenomenon of tucking, where the blade lead edge becomes tucked underneath the blade, losing the frictional sealing relationship required for blade cleaning. These problems require removal and replacement of the blade. Filming on the charge retentive surface may occur even though toner is cleaned from the surface. Filming, which can be a gradual buildup of material on the charge retentive surface can deteriorate image quality. Filming occurs either uniformly or streaking, due to deficiencies in blade cleaning, requiring the use of a lubricant and a balancing abrasion element to prevent filming. A large number of lubricant schemes have been tried to reduce friction to increase life of the blade, reduce wear on the photoreceptor, prevent tucking and minimize toner impaction, including and not limited to various dusting arrangements with dry lubricants, toner additives, coatings and fillings for the blade, etc. While it might appear that a rigid metal blade might solve the problems of rigidity and wear, in fact, the frictional contact required between the surface and blade quickly wears away the blade and any surface lubricants applied thereto. Even when blade cleaning works well, a problem still exists in removing the pile of toner from the charge retentive surface in front of the blade. A large number of toner removal schemes have been proposed, such as vacuum or other air flow arrangements, biased rolls and brushes, augers or electrostatic transports as well as numerous others. All have problems in removing toner from the area adjacent the blade. Of course, blade cleaning also presents numerous other problems, including controlling the accuracy of the alignment of the blade with the charge retentive surface, controlling uniformity of force along the blade edge contacting the charge retentive surface, and design restrictions in desirable orientations and locations along the charge retentive surface for easy removal of toner collecting at the blade.
It is known that a biased member attracts and repels toner, as shown by U.S.-A 4,154,522, to Ikesue, where an electrode on the charge retentive surface attracts toner cleaned from the charge retentive surface to be carried to the development station, U.S.-A 4,286,039 to Landa et al., where a roller is biased to pick up toner, and U.S.-A 3,728,016 to Harbour, Jr. et al. which shows a porous elastomeric wiper which is periodically biased to repel toner adhering thereto. U.S.-A 3,848,993 to Hasiotis suggests an applied voltage to a metal member supporting an elastomeric member in contact with a charge retentive surface to either attract or repel toner at the cleaning edge. U.S.-A 4,481,275 Iseki et al shows that the charge retentive surface may be charged and used to collect toner. Of course, a biased brush member is often used in brush cleaning, where biased fibers in a brush collect toner, and differently biased detoning rolls are used to remove the toner from the brush fibers. U.S. patent application Ser. No. 200,328, filed May 31, 1988, and assigned to the same assignee as the present application, suggests that development of a latent image on a surface might be accomplished from a biased donor roll with an A.C. biased electrode interposed between the donor roll and the latent image-bearing substrate, with the effect of detachment of toner from the surface to create a cloud of toner available for development.
U.S.-A 3,668,008 to Severynse teaches the use of an ionized air flow for the neutralization of charge and removal of toner from a charge retentive surface.
A preclean corotron is sometimes used to neutralize charge on the charge retentive surface prior to removal of toner therefrom, as shown, for example, in U.S.-A 3,572,923 to Fisher et al. which shows a D.C. corotron, although A.C. corotrons have also been used. Image disturbers, to disturb or puddle toner prior to cleaning to make detachment of toner by the cleaner easier, and are characterized by either mechanical devices, which brush against the toner or other arrangements, such as for example, U.S.-A 4,627,717 to Thompson et al., which provides a magnetic field closely adjacent to the charge retentive surface. The use of multiple colors of toner makes cleaning even more difficult, because of the different charge characteristics of the different types of toner, which sometimes requires charge neutralization to deal with the charged state after cleaning.